Field of the Invention
The present invention relates to liquid crystal display devices including touch panels and particularly relates to a liquid crystal display device including an Oncell touch panel.
Description of the Background Art
Display devices, the display surfaces of which have touch sensors that detect inputs by touch operations, have been often used in recent years. A projected capacitance touch panel employs a method of forming a conductive film on a transparent substrate and detecting a variation in capacitance of touches generated in the conductive film. Such a touch panel is configured by, for example, forming conductive films on two substrates individually before sticking these substrates together, forming conductive films on both surfaces of one substrate facing each other, or forming two conductive films on one surface of one substrate.
Attaching the touch panel of the above-discussed configuration to, for example, a liquid crystal display device achieves a display device having a function of input by a touch operation. However, this display device, which is thick in its entirety, has needed to be thin. To meet such a need, an Oncell structure is considered where a sensor pattern composed of a conductive film is directly formed on a liquid crystal cell of a liquid crystal display device and a polarization film is attached outside the sensor pattern (close to the display surface) (e.g., see Japanese Patent Application Laid-Open No. 2012-8255). Meanwhile, although a transparent conductive film has been mainly employed as a material of a sensor pattern for sensor wires of a touch panel or the like, a touch panel used for a large display device is now required to have a low resistance in its sensor wires. Accordingly, the use of a metal wire is considered as a material of the sensor pattern.
However, a polarization axis of light in the vicinity of the metal wire is projected to another axis under the influence of the metal wire when the Oncell structure is applied to a touch panel that uses the metal wire. This results in a change from a state where light should be primarily modulated in a polarization film. In particular, part of light that should be primarily shielded passes through a polarization film when polarization light having a right angle to a polarization axis of the polarization film is projected to the other axis. Unfortunately, this generates a black floating (i.e., a phenomenon where a black portion of an image becomes whitish), thus reducing contrast.
Further, a straight-line metal wire causes striations where a high-brightness light source typified by sunlight scatters and diffracts at edges of the metal wire, thus causing reflection light to spread in a direction orthogonal to the metal wire.
On the other hand, employing a sensor pattern of a non-straight-line metal wire in order to reduce the visibility of the striations is difficult to conform all edges of the metal wire to the polarization axis of the polarization film. Accordingly, when the Oncell structure is employed in order for the display device to be thin in its entirety, a sensor pattern whose metal wire deviates from the polarization axis of the polarization film is formed. Consequently, black brightness rises (the black floating occurs), which causes a reduction of the contrast in an area where directions of the edges of the metal wire deviates from a direction of the polarization axis.